Android Toolbar Navigation Icon Setting Order Issue and Solution

Problem Background and Phenomenon Analysis

In Android app development, Toolbar, as a key component of Material Design, provides a flexible navigation and action interface. However, many developers encounter a tricky issue when customizing navigation icons: despite calling the setNavigationIcon() method and passing a custom Drawable resource, the Toolbar displays the default back arrow icon instead of the expected custom one. This problem typically manifests as the navigation icon remaining unchanged regardless of the Drawable passed, and if setNavigationIcon() is not called at all, no icon appears.

From the provided code example, the developer configures the Toolbar in the Activity in the following order:

Toolbar toolbar = (Toolbar) findViewById(R.id.my_awesome_toolbar);
toolbar.setNavigationIcon(R.drawable.ic_good);
toolbar.setTitle("Title");
toolbar.setSubtitle("Sub");
toolbar.setLogo(R.drawable.ic_launcher);
setSupportActionBar(toolbar);

This configuration seems logical but actually causes the custom navigation icon to be overridden. The root cause lies in the internal mechanism of the setSupportActionBar() method.

Core Mechanism Explanation

Toolbar integrates with the traditional ActionBar through the setSupportActionBar() method. When this method is called, the system converts the Toolbar into the app's standard ActionBar and automatically applies a series of default configurations, including the navigation icon setting. If the Activity declares a parent Activity in AndroidManifest.xml (via android:parentActivityName or android.support.PARENT_ACTIVITY), the system enables back navigation by default and sets the navigation icon to the standard Material Design back arrow.

The key point is that calling setSupportActionBar() overrides any custom icon previously set via setNavigationIcon(). This is because the system reapplies default styles and logic during integration, resetting the navigation icon to the standard one per Material Design guidelines. Thus, even if developers set a custom icon before calling setSupportActionBar(), these settings are cleared during the integration process.

Solution and Code Implementation

Based on the best answer analysis, the core solution is to adjust the order of method calls: first call setSupportActionBar() to complete the Toolbar-ActionBar integration, then set the custom navigation icon. This ensures the custom icon is applied after the system defaults, overriding them. Here is the corrected code example:

Toolbar toolbar = (Toolbar) findViewById(R.id.my_awesome_toolbar);
setSupportActionBar(toolbar);

toolbar.setNavigationIcon(R.drawable.ic_good);
toolbar.setTitle("Title");
toolbar.setSubtitle("Sub");
toolbar.setLogo(R.drawable.ic_launcher);

This order guarantees that the custom icon takes effect after the system default configuration, correctly displaying the developer-specified Drawable. In practical testing, this method works stably on Android 4.4 and above.

Supplementary References and Advanced Usage

Referencing other answers, back navigation can also be explicitly enabled via getSupportActionBar().setDisplayHomeAsUpEnabled(true). This method sets the navigation icon to the default Material Design icon, after which developers can call toolbar.setNavigationIcon() again to override it. For example:

Toolbar toolbar = (Toolbar) findViewById(R.id.signIn_toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
toolbar.setNavigationIcon(R.drawable.ic_chevron_left_white_36dp);

This approach offers a more explicit control flow, especially suitable for scenarios requiring dynamic icon switching. However, note that setDisplayHomeAsUpEnabled(true) itself sets a default icon, so the custom icon must be set afterward.

Complete Implementation Steps

To ensure correct display of Toolbar navigation icons, follow these steps:

1. XML Layout Configuration: Define the Toolbar in the layout file, ensuring its ID and styles meet design requirements. The example uses android.support.v7.widget.Toolbar with basic properties like android:id, android:layout_height, and android:background.
2. Activity Code Initialization: In the Activity's onCreate() method, first obtain the Toolbar instance via findViewById(), then immediately call setSupportActionBar(toolbar) to complete integration.
3. Custom Icon Setting: After setSupportActionBar(), call toolbar.setNavigationIcon() with a custom Drawable resource. Simultaneously, set other properties like title, subtitle, and logo.
4. Parent Activity Configuration: If the app requires back navigation, correctly declare parent Activity relationships in AndroidManifest.xml. This does not affect custom icon display as long as the correct calling order is followed.

Compatibility and Best Practices

This solution is verified on Android 4.4 (API level 19) and above, compatible with AppCompat library v7 and later. For earlier Android versions, use compatibility libraries and test actual effects. Best practices include:

• Always set custom navigation icons after setSupportActionBar().
• Use high-resolution Drawable resources to adapt to different screen densities.
• Combine setDisplayHomeAsUpEnabled() and setNavigationIcon() when dynamic icon switching is needed.
• Unify Toolbar appearance through themes and styles to reduce hardcoding.

By understanding the integration mechanism between Toolbar and ActionBar, developers can avoid common navigation icon setting issues and achieve flexible, design-compliant user interfaces.